The invention relates to projection systems to project mono- and stereoscopic images on a large viewing screen by the optical projection technique.
The proposed projection systems are intended for the consumer-oriented and professional applications in cine-, tele-, video- and computer-projection, projection of theatrical scenery, advertisements, as well as for other purposes. For generating the projected images, the presently-used and proposed updated episcopes, diascopes, cine-projectors, and video, tele- and computer projectors can be used. The proposed reflecting or translucent viewing screens are capable of providing high optical parameters of the screen images and considerable operation capabilities of projection not known in the prior art.
The extensively-used and available projection systems comprise a projector and a projection screen. The front-projection systems serve to project images onto a reflecting (front-projection) screen or a white wall, and the rear-projection onesxe2x80x94to project images onto a translucent (rear-projection type) screen. U.S. Pat. No. 6,600,600 to Chen, Shane; U.S. Pat. No. 6, 609,799 to Myers, Kenneth J.; U.S. Pat. No. 6,543,999 to Covannon et al.; U.S. Pat. No. 6,601,961 to Masaki, Tadahiro; U.S. Pat. No. 6,600,528 to Colgan et al. and U.S. Pat. No. 6,469,830 to Dubin et al disclose variations on projection screen that performs the diffusive scattering.
For example U.S. Pat. No. 6,469,830 teaches that a rear-projection screen has, at the side of projection onto the screen (at the reverse, or rear side of the screen), a lens raster, surface area of all the raster lenses covering the entire surface area of an image (that is projected onto the screen); the screen, at its front side (from the viewers"" side), is provided with a plate having a surface that scatters the light diffusively; on which surface each one of the raster lenses focuses the projection rays; for the purpose to smooth over the viewed brightness uniformity, when viewing an on-screen image, a number of projectors is positioned behind the screen(each of them being positioned at a predetermined projection point to provide a greater density of the image dots (that are focused by the raster lenses), as well as for the purpose to arrange an optimal directional pattern of the viewed on-screen image so that to enhance the on-screen image brightness uniformity (when said image is seen by viewers from different viewing sectors).
The known projectors are described in: Makartsev V. V., Khesin A. Ya., Steierberg A. L., Large-screen video systems, Moscow,  less than  less than Panas greater than  greater than  publishers, 1993, pp. 15-22, 57-83, 96-99, 147-155, FIGS. 1, 2 and 22, 23.
The major disadvantage of the above-discussed projection systems is their large dimensions and considerable weight. This disadvantage is connected with the necessity to carry out projection in a large projection space between a projector and viewing screen at a projection distance that must be not less than the length of the screen image diagonal. Further, there is a possibility that the projection and images on the screen can be shadowed by viewers and objects that are present in this space. The technical paradox is that a reflecting or translucent viewing screen in case of projection of a bright and sharp image must reflect or, respectively, transmit the projected light flux to the maximal extent. Thereupon in viewing the screen images when a viewing screen has an external parasitic illumination, the image contrast deteriorates significantly, brightness is lowered at the edges of the screen image field, and the colour-rendering accuracy is lost. These parameters can be optimal only on a black screen (similar to a black screen of the direct vision kinescopes). In this case, a lower quality of the screen images restrains possibilities to use projection systems in illuminated premises and outdoors. This difficulty is connected with design problems of the modern projection systems that permit the projection within the projection angles (angle of the axis inclination with respect to the viewing screen perpendicular) of not over 30xc2x0.
A rear projection system comprising a lenticular-raster rear projection (translucent) viewing screen is the most proximate one to the claimed invention in terms of the set of the characteristic features and attained technical result. The screen consists of two parts: on the projection side disposed is a Fresnel lens, whereto, on the viewer side, attached are vertically positioned are lenticular elements divided by black vertical strips. The presence of these black strips ensure an image of an high contract even in brightly-illuminated premises. Axial magnification factor (of brightness) of a screen is 5.7 units. A Fresnel lens having a very great axial directivity factor (up to 100) concentrates the projector light flux within a very narrow angle of diffusing. Lenticular lenses direct the concentrated light flux in slots between the black vertical strips, diffusing the same in the viewer direction within a relatively broad observation angle. Thereby an optimum tradeoff of the light concentration (luminous efficacy) and viewing zone width against the screen reflectance is achieved. A dark screen is not sensitive to external illuminations, and an high concentration of light in narrow slots is perceived as an high brightness of an image.
A disadvantage of the rear- and front projection systems is the necessity of a large volume of the projection space, without shadowing by external objects. Further, the lenticular-raster screens are known to reduce significantly the brightness and colour-rendering accuracy from the centre to edges of the screen image, particularly when in viewing at the aspects near to the edge of the viewers"" location sector. Besides, an excessive growth of dimensions and weight of the prior-art rear projection systems is caused by the necessity to place a projection system in a light-protected premises or a housing containing projection mirrors, and the need to have means for rigid suspension of a projector. These problems, and also the need for a longer projection distance between a projector and screen (comparable with the image diagonal length) complicate design of the prior-art rear- and front projection systems and make them more expensive.
The object of the invention is to provide inexpensive small-dimension and lower-weight projection systems having reflecting or translucent viewing screens to project mono- and stereoscopic quality images in any scales of magnification of an image in a bright external parasitic illumination of the screen image.
The common technical result achieved through embodying of the claimed invention is a flat design of a projection system that provides a reduction of the projection space, improvement of the basic parameters and also provides novel parameters of a projection system, with a maximal luminous efficacy by virtue of effecting the projection from the screen end-face.
An additional technical result according to claim 2 is the possibility of the separate or simultaneous frontal and/or translucent projections and viewing of images from two sides of a screen.
Another additional technical result according to claims 3 and 4 is the use of the end-face projection to project the rays into the interior of a screen in the form of a light guide to form a screen image by way of multiple reflection of the rays in a light guide. This approach will exclude shadowing of the projection and that of the pre-screen and post-screen projection space volume.
Still another additional technical result according to claim 5 is formation of a screen image in projection of the rays that correspond to certain image elements (pixels) and characterised with different angles of entrancexe2x80x94incidence on the reflecting surfaces inside a screen so that to output said rays by screen light-diffusers in the appropriate coordinates of a screen image formation.
Still another additional technical result according to claim 5 is broadening of the screen area having an anti-flare protection, or that of the screen""s controlled transparency, and reduction of the area of the screen image visible elements.
Still another additional technical result according to claim 6 is a reduction of the projection space or the light-guide screen thickness by the optical narrowing of longitudinal section of the projection rays using the projectors"" projection lenses.
Still another additional technical result according to claim 7 is a reduction of the projection space or thickness of the light-guide screen by the optical narrowing of longitudinal section of the translucing projection rays in the illumination system of a transparency projector, without the use of projection lenses.
Yet another technical result of application of the invention according to claim 8 is the possibility of an easy viewing of stereoscopic images, without the use of stereoscopic spectacles, to be provided for a moving viewer, as well as the possibility of simultaneous viewing of different images by different viewers on a common screen at various aspects of observation of images.
Said technical effect of embodying the invention is to be achieved as follows: A projection system comprises one or a number of projectors for generation and/or projection of transformed and/or trapezoid image frames, and a viewing screen. The optical elements are arranged on the view screen, have entrance windows for capturing projection rays and are configured to reflect or deflect the projection rays via exit windows into a sector of observation. A distinguishing feature is that the entrance and exit windows have an area that is multiple times smaller than the screen area around the entrance and exit windows, and an optical system is provided to register cross sections of the projection rays with the entrance windows of the optical elements, and the optical elements are configured to capture the projection rays directed from an end-face of the viewing screen across its surface.
The distinction is in that the light-diffusers are implemented in the form of optical elements adapted to capture the projection rays directed from the screen end-face along the screen plane and, subsequently, reflect or deflect, optically, said rays, with simultaneous diffusing of the same, into the sector of the screen image viewing. For optical magnification and ensuring a projection sharpness depth over the entire screen area, the projectors and viewing screens are provided with an optical system to transform the projection images and to narrow cross-section of the projection rays to the width of entrance windows of the light-diffusers.
In other words, the claimed projection system, comprising one or several projectors and a viewing screen, whereon light-diffusers of the projection rays are provided, is characterised in that the light-diffusers are designed to capture the projection rays directed from the screen end-face along its surface and, subsequently, deflect, optically, said rays, with simultaneous diffusing of the same, into the sector of viewing of an image formed on a screen, and further comprises an optical system that transforms the projected image and matches cross-sections of the projection rays with the entrance pupils of the light-diffusers provided on the screen, so that to provide a sharpness depth of the projected image over the entire surface of the screen.
According to claim 2, the viewing screen is designed to carry out projection from the screen end-face onto the frontal and/or the reverse (from the viewer""s side) surface of the screen, and for said purpose the light-diffusers are implemented in the form of protruding from, or recessed in the screen surfacexe2x80x94mirrors, lenses, prisms for capturing, deflecting or diffusing of the rays projected from the screen end-face. Id est, the projection system is characterised in that the viewing screen is implemented as having the end-face reflectors of the projection, and/or the projectors are disposed at the screen end-face to carry out projection onto the frontal (from the viewer""s side) and/or reverse surface of said screen. The light-diffusers are designed in the form of protruding from, or recessed in the screen surface, optical elements. These elements are implemented in the form of lenses, prisms that completely capture all projection rays that are incident upon the surface of the screen image formation.
In another embodiment of the protection system according to claim 3, the projection system is characterised in that the viewing screen is provided with a light guide in the form of a flat-parallel plate, or a laminate or multi-strip light-guide. The light-guide core has a constant refraction index and has the end-face transparent entrance windows for inputting the parallel projection rays into the light guide. On the light-guide surface, locally over the screen area, disposed are dot-shaped or linear light diffusers to output the projection rays out of the light guide within predetermined coordinates of the screen image formation. Thereafter these light guides diffuse these projection rays into the screen image viewing sector. A projector or projectors are provided with an optical system for forming narrow parallel projection rays and for supplying these rays through the light-guide end-faces into predetermined coordinates or incidence of the rays upon the light-guide planes. Such arrangement ensures propagation of the rays inside the light guide up to certain light diffusers owing to multiple internal reflection from the light-guide surfaces, free from the screen light diffusers. Some projection rays, captured by appropriate light diffusers, exit from the light guide and are diffused into the screen image viewing sector.
According to claim 3, in the viewing screen, the light-guide core is implemented as having the narrowed, wedge-wise, light-guide thickness in from the light guide""s entrance end-face in the direction of propagation of rays in the light guide. The core has a constant refraction index and is coated with a cladding or an optical entrance window of a light diffuser having a constant or stepped refraction index whose value is lower than that of the core. For any of these versions of embodiment of the light-guide screen, a projector is provided with an optical system for formation of projection of rays of the projected image""s various elements, which rays are characterised by different angles at which angles these rays enter the light-guide end-face. Such arrangement provides a selective output of these rays out of the light guide by the screen light diffusers within the appropriate coordinates of formation of a screen image. Then these rays are diffused into a sector of observation of the image.
According to claim 4 of the invention, the projection system is characterised in that the entrance and exit windows of the screen""s light diffusers have a minimal area, that is multiple times smaller than the screen area around the windows. In one embodiment, the screen area around the exit windows on the screen is coated with an opaque anti-flare black layer. In another embodiment, on the screen area between the light diffusers, an opaque anti-flare black mesh is disposed. In the third embodiment, the screen area around the light diffusers is optically transparent or coated with a photochrome film to adjust transparency of the screen using the ultraviolet background illumination.
According to claim 5, the projection system is characterised in that the projector is equipped with a projection telephoto lens and anamorphotic cylindrical lens, or a cylindrical mirror for a minimal magnification of the projection size, for example a magnification in height, and for simultaneous magnification of the projection to the screen width. The projector is positioned at a predetermined distance from the screen, and on the end-face of the screen width positioned is a mirror retrodirective reflector to deflect the projection from said end-face over the screen surface. In another embodiment, the projector or projectors are disposed near the screen end-faces, and on the screen end-faces positioned are the mirror reflectors for multiple reflection of the projection. These embodiments provide the optimal narrowing of cross-section of the projection rays within the area of the light diffusers"" entrance windows.
According to claim 6, the projection system is characterised in that a transparency projector and a screen are provided with an optical system to transform the projection images and to narrow cross-section of the projection rays without the use of projection lenses and transforming anamorphotic lenses. For this purpose, in the transparency projector, an illuminator of the transparent projected images is provided with an optical system for formation of the background illumination of slides by thin, fan-wise diverging rays, cross-sections of the rays being broadened within sizes of area of entrance windows of the light diffusers.
According to claim 7, the projection system is characterised in further comprising one or several stereo projectors and a stereo screen having light diffusers and a lenticular stereo raster. The stereo raster is intended for spatial selection of the left and right images of a stereo couple to the zones of vision of the stereo couple""s left and right images by, respectively, the viewer""s left and right eyes. For easy, without spectacles, viewing of stereo images from at aspect or in case when viewers move laterally, the system is provided with a semi-automatic manually-controlled corrector, In another embodiment, the system is provided with an automatic corrector coupled to a sensor for tracking the viewers"" eyes coordinates. Said semi-automatic or automatic correctors comprise a drive for carrying out various methods of correcting the stereoscopy system, for example by way rotating the stereo screen about its vertical axis, or by displacing the lenticular raster, or displacing the stereo projectors along the screen. This arrangement also provides the optical automatic conjugation of zones of vision of the images, stereo couples with the viewer""s left and right eyes when a viewer moves, and also provides the possibility of simultaneous viewing of different images by different viewers in different observations aspects.